Re: [PATCH v5 2/3] VT: Add KDFONTINFO ioctl

On 4/17/24 19:37, Alexey Gladkov wrote:
> Each driver has its own restrictions on font size. There is currently no
> way to understand what the requirements are. The new ioctl allows
> userspace to get the minimum and maximum font size values.
>
> Acked-by: Helge Deller <[email protected]>
> Signed-off-by: Alexey Gladkov <[email protected]>
> ---
>   drivers/tty/vt/vt.c       | 24 ++++++++++++++++++++++++
>   drivers/tty/vt/vt_ioctl.c | 13 +++++++++++++
>   include/linux/console.h   |  3 +++
>   include/linux/vt_kern.h   |  1 +
>   include/uapi/linux/kd.h   | 14 ++++++++++++++
>   5 files changed, 55 insertions(+)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 9b5b98dfc8b4..e8db0e9ea674 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -4851,6 +4851,30 @@ int con_font_op(struct vc_data *vc, struct consol=
e_font_op *op)
>   	return -ENOSYS;
>   }
>
> +int con_font_info(struct vc_data *vc, struct console_font_info *info)
> +{
> +	int rc;
> +
> +	info->min_height =3D 0;
> +	info->max_height =3D max_font_height;
> +
> +	info->min_width =3D 0;
> +	info->max_width =3D max_font_width;
> +
> +	info->flags =3D KD_FONT_INFO_FLAG_LOW_SIZE | KD_FONT_INFO_FLAG_HIGH_SI=
ZE;
> +
> +	console_lock();
> +	if (vc->vc_mode !=3D KD_TEXT)
> +		rc =3D -EINVAL;
> +	else if (vc->vc_sw->con_font_info)
> +		rc =3D vc->vc_sw->con_font_info(vc, info);
> +	else
> +		rc =3D -ENOSYS;
> +	console_unlock();
> +
> +	return rc;
> +}
> +
>   /*
>    *	Interface exported to selection and vcs.
>    */
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 4b91072f3a4e..9a2f8081f650 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -479,6 +479,19 @@ static int vt_k_ioctl(struct tty_struct *tty, unsig=
ned int cmd,
>   		break;
>   	}
>
> +	case KDFONTINFO: {
> +		struct console_font_info fnt_info;
> +
> +		memset(&fnt_info, 0, sizeof(fnt_info));
> +
> +		ret =3D con_font_info(vc, &fnt_info);
> +		if (ret)
> +			return ret;
> +		if (copy_to_user(up, &fnt_info, sizeof(fnt_info)))
> +			return -EFAULT;
> +		break;
> +	}
> +
>   	default:
>   		return -ENOIOCTLCMD;
>   	}
> diff --git a/include/linux/console.h b/include/linux/console.h
> index 31a8f5b85f5d..4b798322aa01 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -21,6 +21,7 @@
>   #include <linux/vesa.h>
>
>   struct vc_data;
> +struct console_font_info;
>   struct console_font_op;
>   struct console_font;
>   struct module;
> @@ -102,6 +103,8 @@ struct consw {
>   	bool	(*con_switch)(struct vc_data *vc);
>   	bool	(*con_blank)(struct vc_data *vc, enum vesa_blank_mode blank,
>   			     bool mode_switch);
> +	int	(*con_font_info)(struct vc_data *vc,
> +				 struct console_font_info *info);
>   	int	(*con_font_set)(struct vc_data *vc,
>   				const struct console_font *font,
>   				unsigned int vpitch, unsigned int flags);
> diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
> index d008c3d0a9bb..383b3a4f6113 100644
> --- a/include/linux/vt_kern.h
> +++ b/include/linux/vt_kern.h
> @@ -33,6 +33,7 @@ void do_blank_screen(int entering_gfx);
>   void do_unblank_screen(int leaving_gfx);
>   void poke_blanked_console(void);
>   int con_font_op(struct vc_data *vc, struct console_font_op *op);
> +int con_font_info(struct vc_data *vc, struct console_font_info *info);
>   int con_set_cmap(unsigned char __user *cmap);
>   int con_get_cmap(unsigned char __user *cmap);
>   void scrollback(struct vc_data *vc);
> diff --git a/include/uapi/linux/kd.h b/include/uapi/linux/kd.h
> index 8ddb2219a84b..68b715ad4d5c 100644
> --- a/include/uapi/linux/kd.h
> +++ b/include/uapi/linux/kd.h
> @@ -185,6 +185,20 @@ struct console_font {
>
>   #define KD_FONT_FLAG_DONT_RECALC 	1	/* Don't recalculate hw charcell s=
ize [compat] */
>
> +/* font information */
> +
> +#define KD_FONT_INFO_FLAG_LOW_SIZE	_BITUL(0) /* 256 */
> +#define KD_FONT_INFO_FLAG_HIGH_SIZE	_BITUL(1) /* 512 */

Do we really need those bits?
You set a default min/max font size in con_font_info() above,
and all drivers can override those values.
So, there are always min/max sizes available.

> +struct console_font_info {
> +	__u32  flags;			/* KD_FONT_INFO_FLAG_* */

One space too much in front of "flags" ?

> +	__u32 min_width, min_height;	/* minimal font size */
> +	__u32 max_width, max_height;	/* maximum font size */
> +	__u32 reserved[5];		/* This field is reserved for future use. Must be =
0. */
> +};
> +
> +#define KDFONTINFO	_IOR(KD_IOCTL_BASE, 0x73, struct console_font_info)
> +
>   /* note: 0x4B00-0x4B4E all have had a value at some time;
>      don't reuse for the time being */
>   /* note: 0x4B60-0x4B6D, 0x4B70-0x4B72 used above */